Fish netpen

ABSTRACT

A netpen for breeding, storage or transport of fish in the sea, in particular completely or in part in open sea regions outside the skerries is provided. The netpen may be lowered in the sea to a desired depth. The netpen may be elevated to a half or approximately half submerged state for various work operations, such as maintenance and inspection of the netpen or harvesting. The netpen has a substantially spherical geometry. The netpen consists of a framework of stays, a horizontal through center pole also serving as a buoyancy adjusting element for elevation and lowering of the netpen, a horseshoe-shaped working platform having an integrated dock for working vessels. The entire working platform including dock is liftable and lowerable through buoyancy adjustment using a designated element. The working deck is mounted on an extended axle on the center pole. The netpen may be rotated inside said working deck.

RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing ofInternational Application No. PCT/NO2004/000035 filed on 6 Feb. 2004,which claims priority to Norwegian Patent Application No. 2003 0592filed on 6 Feb. 2003 in Norway. The contents of the aforementionedapplications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a netpen or enclosure for breeding,storage, or transport of fish in the sea. More particularly, the netpenof the present invention is designed for use in open sea regions outsidethe skerries, where the environmental loads are much greater than infjords and other regions in sheltered waters. The netpen may be letfurther down in the water when needed in order, for example, to protectthe fish during algal invasions, temperature variations, etc., and toprotect the installation and the fish from destructive wave forces atthe surface. Further, the netpen may be elevated to a semi-submergedstate for maintenance, inspection, or harvesting, and the ability of thenetpen to rotate, as well as its docking station for vessels andpersonnel working platform, will help enabling maintenance operationsand harvesting to be carried out in an efficient and safe manner.

BACKGROUND OF THE INVENTION

During the past 30 years, marine breeding has seen a formidable growththrough establishment in countries naturally suited for fish farming,such as Norway, Chile, Canada, Ireland, and Japan. These countries havebeen able to offer easily accessible fish farming localities being wellprotected from the most wearing environmental forces in their longfjords, bays, or other regions of sheltered waters. Today, theaquaculture industry in these countries has grown to become a verysuccessful industry.

In the last few years, several expert groups have concluded that theinternational growth potential for the industry is huge. This is thecase not only for those breeds that are already being raised, butnonetheless for new breeds that will gradually grow to become successfulcommercial products. Moreover, it is also expected that the demand forfish and fish products will increase as a result of the rapid populationgrowth. Internationally, among experts, it is commonly agreed upon thatthe main growth in the world's fish production must occur within seafarming, as the total take in the fisheries are approaching an upperdefensible limit of about a 100 million tons per year.

An absolute requirement for further growth within the aquacultureindustry is that the production capacity can be increased, and then formore breeds of farmed fish. With the current situation for theinternational fish farming industry, the potential for increasing theproduction capacity is very limited. This is due to the global lack ofavailable sheltered inner coastal areas, and to that the existingtechnology is unable to provide for an efficient, safe, and profitablefish farming in open sea regions.

With the existing technology, coastal states without any form of, orwith limited access to inner sheltered sea regions, are not able todevelop large scale marine breeding. Existing fish farming installationscommonly have a very simple configuration, generally including a seinefreely suspended from a framework on the surface. Even at relativelyslow current velocities however, the seines of these netpens undergoesappreciable deformations. At more exposed localities, the deformationsmay become severe. In addition, maintenance work and harvestinggenerally are both time consuming as well as expensive. Huge, heavy, andunmanageable seines also present a problem in connection with cleaning,impregnation, and replacement of the seine, as well as duringharvesting. If the seine becomes damaged or worm, it is necessary toreplace the entire seine or to bring it onshore for repair, which alsoinvolves removing the fish from the netpen. Furthermore, somemaintenance operations require that parts of the work are performedunder water, necessitating the use of expensive divers. This work ispotentially dangerous.

The existing fish farming industry also has a problem in that diseases,infections, algal invasions, and various natural phenomena, such as“Super Chill”, air horns, and the like put stress on and kill the farmedfish, which every year brings along great losses for the breeders. Thecause of these problems is a combination of insufficient technology, thefish farming localities, and natural phenomena. Open sea breeding assuch can be beneficial to the fish. Increased current velocity willensure a good water throughput rate in the netpen, result in a greateroxygen uptake and better trim for the fish, as well as an increasedwater replacement and thereby less fouling inside the netpen. Inaddition, the water temperature and salinity are generally more stablein the open sea outside the skerries. These are all factors that mightimprove the welfare, health and reproduction of the fish.

Outside the fish farming installations, the environment is contaminatedby debris or waste, such as fodder residues and excrements from thefarmed fish. Such waste (nutrients) accumulates in such big amounts thatit is effectively pollution, and is thereby a problem both for marineanimals as well as for human beings that travel in the sheltered waterregions. In addition, many people also find the fish farminginstallations visually offensive.

Besides contributing to free up regions in sheltered waters and reducethe area conflicts, open sea fish farming also will provide beneficialenvironmental effects. Larger water depths, more rapid currents, and agreater distance to the shore will result in a reduction of thecontamination of the sea floor and the inshore zone, as well as in arelief of the threat against wild extermination-threatened fish breeds,such as the wild salmon, for example.

As a consequence of the above problems, many people are convinced thatthe most important factor for a future sustainable growth within theaquaculture industry will be the ability to establish fish farms in theopen sea outside the skerries. This would make possible the operation ofa sound breed of a larger number of fish species in more countries,regardless of whether or not the particular country has access to asheltered coastline.

Internationally, several attempts have been made at providing fishfarming installations intended for deployment in open sea. Unfortunatelyhowever, none of these attempts have resulted in a commercially viableinstallation for operationally efficient, safe, and profitable fishfarming outside the skerries. A few of the installations have had alimited commercial success however, although in more sheltered regions.The present situation confirms this in that the occurrence of open seafish farms is in fact very limited, in spite of the fact that stateshaving an exposed coastline have expressed high ambitions of running alarge scale fish farming. Generally, the previous attempts atestablishing open sea fish farming installations have failed because theinstallations have suffered from one or more essential shortcomingspreventing a safe, ethical, and economically lucrative fish breeding.The most successful approach to an open sea fish farming installation isbelieved to be an installation provided by the American company OceanSpar Technologies, disclosed in the U.S. Pat. No. 5,617,813. Thisinstallation has been used for fish farming in, among other countries,Hawaii, Ireland, and the United States of America. However, even thoughthe installation has been utilized for raising a few broods of fish, itdoes by no means provide any substantial contribution to the large-scaleestablishment of aquaculture industry in the open seas outside theskerries. The shortcomings of the installation are, among other things,that it is difficult to maintain as much work must be performed underwater by divers, that it is difficult to harvest the fish, that one haspoor visual control of the fish from the surface, that it is impossibleto dock to the installation with larger boats without damaging theinstallation, that the seine needs to be cleaned under water, that eachday dead fish must be picked up by divers, and that the installation islimited in depth to about 35 meters, owing to the divers.

The U.S. Pat. No. 4,312,296 describes a spherical netpen. Thisinstallation never became a commercial success. The netpen is verysmall, having a volume of about 1200 m³. The construction is composed ofaluminum stays and a grating or lattice. Aluminum as constructionmaterial is very rigid and brittle, and therefore susceptible tofatigue, which is unfavorable when the concept is to be implementedoffshore, where the environmental loads are continual, cyclic, andlarge. In addition, this installation may only be lowered to slightlybelow the surface, and is thus exposed to considerable wave loading.

Moreover, the installation neither includes a working platform forpersonnel nor a docking station for boats.

The U.S. Pat. No. 4,312,296 relates to a spherical netpen having avertically extending center pole.

The PCT application WO 92/03921, like the U.S. Pat. No. 4,312,296,relates to a spherical netpen having a through center pole. This netpenobviously bear close resemblances to the one in the above patent, boththe construction material and the arrangement for buoyancy controlthrough separate floatation bodies in each end of the center pole beingidentical.

The U.S. Pat. No. 5,617,813 relates to a netpen having a vertical centerpole, as well as a weighting organ attached thereto.

Even today, examples are found of netpens that are being used for otherpurposes than fish farming, such as for storing various kinds of wildfish. The most common case is that inshore fishermen store the fish innetpens while awaiting delivery to an onshore reception facility. It canbe easily appreciated that this use of netpens would be much morewidespread if cost effective, efficient and enduring netpens becameavailable for use in open sea. A future scenario could be that fishingboats deliver their catch, or parts thereof, on a regular basis to hugenetpens by the fish fields outside central marketing places, therebymaking it possible both to adapt to the current demand and to at anytime deliver ultra fresh, or even living fish. A netpen having apermanently outstretched seine could also be used in transporting hugeamounts of living fish. Currently, huge amounts of living fish are beingtransported in fish carrier boats or seine bags. However, a problemassociated with such transport is that the fish are put under stress dueto a large density of fish per m³. Transporting fish in a permanentlyoutstretched netpen will not put the fish under the same stress, makingit feasible to transport the fish over great distances, such as tunafish from Europe to Japan, for example.

SUMMARY OF THE INVENTION

Hence, a need exists for a fish farming installation that is suited foroperation in a marine environment corresponding to open sea regionsoutside the skerries, wherein good conditions can be maintained for fishand installation continuously throughout the year, and wherein goodworking conditions for personnel is maintained with sufficientcontinuity so that the breeding can be carried out efficiently andsafely as an all-year activity. Preferably, it should be possible to letthe installation downwards in the water in order to avoid toxic algaeand to protect the installation and the fish during extreme weatherconditions. Further, the installation must be constructed in a mannerthat enables all operational tasks to be carried out in an efficient andsafe manner, and the installation must have a size that is sufficient toallow for commercial breeding and other activity to be carried on with agood profitability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 3, and 4 show the netpen without a seine from different angles,depicted in a view diagonally from above, in a side view, and in a frontview, respectively. The netpen is partially encircled by ahorseshoe-shaped working deck 6. The buoyancy adjustment for the netpenoccurs in the center pole 5, which extends transversally across thenetpen, while the buoyancy adjustment for the working platform 6 iscontrolled by the same center pole in addition to the stay 13, whichcould be a tube, for instance. The working deck 6 is in horizontalposition only when the netpen is semi-submerged for maintenancepurposes.

FIG. 2 shows the netpen covered with a seine 12.

FIGS. 5 and 6 show the configuration of the framework and center pole 5of the netpen, depicted in a side view and a front view, respectively.The netpen consists of centre stays 1, intermediate stays 2, polar stays3, tie bars 4, and the center pole 5.

FIG. 7 shows a possible embodiment of the center pole 5, having threeseparate compartments for buoyancy adjustment.

FIG. 8 shows the horseshoe-shaped working deck 6 viewed from above. Thedeck itself will be dressed with a grating, which is not depicted in thedrawing.

FIG. 9 is a side view showing the working deck 6 and the docking station7. The drawing depicts a possible truss for the working deck 6, theslide bearings 16 that are attached to the center pole 5, and the stay13 for adjusting the buoyancy of the working deck and the dockingstation.

FIG. 10 shows a possible embodiment of the terminal unit 14 of thecenter pole 5, including a gear rim 18 for power transmission duringrotation of the netpen, a rotary shaft 15, and bushing collars 19.

FIG. 11 shows the terminal unit 14 in a side view, not including thegear rim 18 but including the bushing collars 19 and the rotary shaft15.

FIG. 12 shows a possible embodiment of the connection points 11 betweenthe tie bars and all the vertical stays of the netpen framework.

FIG. 13 is a side view showing the netpen in a surface position. About1/10 of the netpen diameter extends above the water surface. Reservefloatation buoys 10 with weighting organs 9 are provided at the frontand the back of the netpen.

FIG. 14 is a front view showing the netpen in an operative position(surface position or fully submerged).

FIG. 15 is a side view illustrating rotation of the netpen inside theworking deck 6.

FIG. 16 shows a possible solution for attaching the seine 12 to theframework.

FIG. 17 shows a possible design of three different netpen modules thatmay be used for covering the netpen with a seine.

FIG. 18 shows a possible attachment of the netpen modules to theframework, wherein the modules can be attached by means of a rail system25 in the different windows of the netpen framework.

FIG. 19 is a rough detail drawing showing how the seine attachment canbe implemented using balls 24 and cut cylinders 25, and how these can beattached to the netpen framework by way of a coupling plate 26.

FIG. 20 shows a principle drawing for a sway-anchoring, wherein 29 isthe netpen, 30 is an external floatation unit, 28 is the uppermost partof the anchoring line, 27 is the lowermost part of the anchoring line,and 41 is the anchor.

FIG. 21 is a principle drawing illustrating how harvesting or sorting offish can be carried out by mounting a seine or grating 31 in the netpencross-section located above the water surface, and subsequently rotatingthe netpen.

FIG. 22 shows how the energy platform 30 in the preferred embodiment ofthe invention is positioned relative to the netpen 29 and a mooredvessel 32.

FIGS. 23 and 24 are a view seen diagonally from behind and a front view,respectively showing a possible design of the energy platform 30.

FIGS. 25 and 26 show two alternative netpen designs in a view diagonallyfrom above.

FIG. 27 shows two netpens connected through the working deck 6.

FIG. 28 shows the positioning of the netpen 29 and the energy station 30relative to the water surface and the anchoring 27 and 28.

FIG. 29 shows the netpen with an additional buoy 23 having a fixedpermanent buoyancy. In the surface position of the netpen, this buoywill float freely tied to the netpen. In this position, the buoy servesno important purpose; not until the netpen is fully submerged the buoy23 will contribute to the stabilization of the netpen, see FIG. 30.

FIG. 30 shows how the stability and depth adjustment of the netpen areattended to in a fully submerged position by means of an additional buoy23 and the reserve buoyancy of the energy platform 30.

FIGS. 31 and 32 show an alternative approach to provide for thestability and depth control of the netpen. From the netpen there aresuspended two long lines 8 with weighting organs 9, which at a givendepth will contact the sea floor, whereupon the weight release willcause the netpen to stabilize at a given depth.

FIGS. 33 and 34 show the principle by which the tie bars 4 are supposedto provide for the stability of the installation. Seven of the tie barshave three openings 38 and 40 through which air and water may pass,whereas one tie bar only has two openings 38. When the installation isbeing submerged, the stay having only two openings is the topmost oneand is located in the center, see FIG. 4. This stay will, when thenetpen is submerged, capture air in an air pocket 39, as shown in FIG.33. Inside the other seven stays the water level will be equal to thesurrounding water level, as shown in FIG. 34.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 show a possible embodiment of the invention. In theconstruction shown, the netpen framework is composed of tubularpolyethylene stays 1, 2, 3, and 4, and a tubular steel center pole 5.The center pole may also be constructed of another rigid and strongmaterial. The stays may be tubular, solid, or have another geometricalshape, such as quadrilateral. Polyethylene, as the material is referredto herein, is also intended to include other plastic materials bearing aclose resemblance to polyethylene. Further included are polyethylene orpolyethylene-like materials containing a certain amount of otherconstituent materials, such as fiber or fiber-like materials, e.g.carbon fiber.

The framework of FIGS. 1-6, when covered by the seine 12, forms a closednetpen, as shown in FIG. 2. The framework is built up of center stays 1,intermediate stays 2, polar stays 3 and tie bars 4. A possible design isshown in FIGS. 1-6, including one center stay, two intermediate stays,two polar stays, and eight tie bars. However, a lower or higher numberof tie bars and vertical stays is also contemplated. Two alternativedesigns for the netpen framework are shown in FIGS. 25 and 26. These aretwo possible ways of increasing the volume of the spherical netpenwithout increasing the height (diameter) of the spherical netpen, whileat the same time the deviations from the spherical shape are not greaterthan that most of its properties, e.g., with respect to symmetrical loaddistribution and rotatability, is maintained. Further, each single staycould be composed of several connected smaller stays. For instance, thecenter stay could be made up of two or more stays that are welded orotherwise coupled together. The stays that are included the frameworkare welded or otherwise coupled together in such a manner that they forma spherical or substantially spherical structure. In this connection itmay be noted, for example, that the plastic rings of the structure notnecessarily need to be perfectly circular; instead, they could have anoval or substantially oval-cross section, and be shaped as a polygonhaving many straight or substantially straight sides.

Across the netpen there extends a rigid center pole 5, FIG. 7. All thetie bars 4 are connected to the center pole 5 at the terminal units 14(FIGS. 10 and 11). The vertical stays can be coupled to the tie bars,for example, by a connection 11 as shown in FIG. 12. Seven of the tiebars 4, and all the vertical stays 1, 2, and 3, are preferably open, sothat water freely can enter into and exit these stays.

However, these stays may also be used for buoyancy adjustment in thatwater is taken in or expelled by means of pressurized air through valvesprovided in the stays to one or more separate chambers. The center pole5 is the load-bearing member for the entire structure. The pole ensuresthat the shape of the netpen is maintained even under extreme loads, andalso controls the buoyancy of the overall structure and connects thenetpen with the working platform 6. The actual buoyancy adjustment isachieved in that the center pole 5 is divided into multiple chambers(see FIG. 7) filled with either water or air. The regulation of thesechambers is performed either manually from the energy station 30 or byremote control.

FIGS. 28-34 show how the stability of the structure is ensured in twooperating positions; a surface position and a fully submerged position.The stability of the structure in the direction parallel with the centerpole 5 is preferably provided for through adjustment of the center pole5 and the positioning of the floatation devices 10, and the working deck6. The working deck 6 is heavy, and consequently, being suspendedunderneath the netpen, will result in a low center of gravity for thestructure. Adjustment using air and water in the center pole 5 ensuresthat the structure exhibits a slightly negative buoyancy. The entirestructure then will be supported by the reserve buoyancy of the buoys.During extreme conditions, the netpen will be let deeper down in thewater. The netpen will then be supported by the reserve buoyancy of theadditional floatation buoy 23 and of the energy station 30, as shown inFIG. 30. Alternatively, the stability in the direction parallel with thecenter pole 5 could be provided for by two weighting organs 9 suspendedbelow the netpen, on extended lines 8. When the installation has aslight negative buoyancy, it will sink downwardly until the weightingorgans 9 land on the sea floor. The weight load on the netpen is thenreduced, and the netpen stabilizes at a particular depth. The length ofthe line 8 may be adapted to the particular depth at which it is desiredto stabilize the netpen in the fully submerged position. The stabilityin the transverse direction of the center stay is ensured by that thetie bar 4, which is located on top and in the center, only has twoopenings 38, FIG. 33 and FIG. 4.

During the lowering from the semi-submerged position to the surfaceposition or the fully submerged position, this stay will capture air ina pocket 39, whereas the other stays will be filled with water (FIG.34). The stay having the air pocket 39 then will serve as a floatationbody and result in a restoring moment for the netpen.

Round the netpen there is mounted a working platform 6, FIGS. 1-4 andFIGS. 8-9. The working platform 6 consists of a truss, preferably madeof steel, and at the top side a flat covering or deck of steel gratingis provided. However, both the truss and the grating may be made ofanother material than steel, such as polyethylene or a compositematerial. At the docking station 7 and the working platform 6 there areprovided bollards and fenders 17, among other things, for obtaining asatisfactory mooring of boats, as well as hand railing and emergencyladders for personnel (not shown in the figures).

The working platform 6 preferably is horseshoe-shaped, but may also beextended to become a circle. The platform is attached to the netpen atonly two permanent fixation points 16 (FIGS. 8-11 and 13), so that thenetpen can be rotated inside the working deck. The attachment occurs inthat an axle 15 being mounted on the terminal unit 14 of the center poleis guided into a bearing 16, such as a slide bearing, on the workingplatform 6. The rotation of the netpen can then be accomplished bypushing the netpen structure around when it is only attached at twoopposing bearings 16, see FIGS. 8 and 15. The actual rotation occurs inthat a motor or hand crank and a transmission are attached to theworking deck and engage the toothed wheel 18 on the terminal unit 14 ofthe center pole 5, FIG. 10. In normal operation, when the netpen is notto be rotated, the working platform 6 will hang vertically and thus belocated underneath the netpen. The positioning of the working platformrelative to the netpen is determined by the floatation stay 13, which inthe preferred embodiment is a tube. This tube comprises chambers,allowing the buoyancy to be adjusted using water and air.

So that the personnel shall be able to get from a vessel to the workingdeck, the working platform 6 is equipped with a docking station 7. Thepositioning of the docking station relative to the netpen and the energyplatform 30 enables an easy and safe docking of vessels 32 to theworking platform, even in relatively rough sea, FIG. 22. The vesselswill attach a long mooring 33 to the energy station 30 and lie parallelwith the center pole 5 and the docking station 7, while at the same timethe vessel 32 is moored to the working platform 6 and the dockingstation 7. This mooring approach ensures that the bow of the vessel 32is facing any waves and currents. In addition, the contact and forcetransmission between the vessel and the netpen will be minimized, whichreduces the chance of conflicts and damage.

The fish is kept enclosed in the netpen by covering the framework bymeans of a seine or a grating 12 (FIGS. 2 and 16-19). In the following,mention made of seine or seine modules preferably refers to seine madeof polyamide synthetic fiber materials, even though other materials,such as other synthetic fiber materials or metal or plastic gratings,shall not be excluded. A possible solution for the seine of the netpenis as follows: Several seine modules are used for covering theframework. The various stays define a number of windows in theframework. FIG. 17 shows the different seine modules that can be usedfor covering the entire framework. In this case three different seinemodules are provided, but other module divisions are possible. Forexample, these three modules may form one module. The attachment for theseine module is preferably accomplished by means of a system comprisingplastic rings 21, rope 22, and zip-fasteners. Along all the stays in theframework, a rope 22 is attached having plastic rings 21, and in theseine modules there are also attached plastic rings, through whichplastic rings a rope is threaded, FIG. 16. When tightening the rope, theseine modules will be strapped and fastened to the framework. In orderto cover the gap between the framework and the seine, the seine modulesare provided with a zip-fastener along their edges. Thus, the seinemodules of different windows can be attached to each other by means of azip-fastener. An alternative attachment for the seine modules is a railsystem 25 attached to the stays in the framework and balls 24 attachedto the seine modules. FIG. 19 shows how these balls 24 may be threadedinto a cut cylinder 25, and thereby help keeping the seine fixed andoutstretched. Said balls 24 preferably are compact balls made ofpolyethylene, whereas said cylinder 25 preferably is made of metal.Polyethylene is preferred for the balls due to its low cost andmaintainability. The cylinder must be able to withstand frictionwearing. The cylinder is attached on the side surface of the stays ineach window by means of a connector plate 26, as shown in FIG. 19, andmay be fixed to the framework by welding, bolting, or clamping. The railsystem for attachment of the seine is preferably realized by mounting ineach window several cylinders 25 (FIG. 18) spaced some distance apart,which distance is sufficiently small to prevent the balls 24 fromdropping out. This will make the rail system more flexible and allow forlarger deformations. It is also possible to use an entire rail in eachwindow. The rail system may be adapted to any possible design of theabove seine modules. Moreover, the rails do not need to be attached atthe side surface of the stays in the framework, but may also be locatedat the front surface or at the back surface thereof.

FIG. 20, as well as FIGS. 22-24 and 28-32, show an energy station 30moored to the netpen 29 in one end and to an anchor in the other end.The energy station 30 contains, among other things, a huge foddercontainer 35, air compressor, aggregate, monitoring equipment, and ahaunt 34 for the personnel. Extending alongside the anchoring line fromthe energy platform 30 to the netpen 29, a lifeline 28 carries fodder,information, air, and energy. The fodder tube runs to one or morefeeding points, preferable located high up on the streamside of thenetpen, against which incoming currents first hits, but other feedingpoints are possible as well, such as at the top of the sphere.

Various anchoring systems may be used. One possible approach is the useof a so-called sway anchoring as shown in FIG. 20, wherein theinstallation 29 is allowed to move freely about a single anchor 41. Theanchoring line 27 and 28 can be attached to an energy station 30, or toa buoy or another floatation device that ensures that the anchoringforces is transferred to the installation as horizontally as possible.The horizontal part 28, as well as the vertical part 27 of the anchoringline may be subdivided into multiple single lines. Another possibleanchoring approach is to make use of two or more main lines (two or moreanchors) in the same or substantially the same manner as saidsway-anchoring alternative. In that case the installation would not beable to move freely all the way around the anchors. A third anchoringapproach that could be used is a so-called tension leg anchoring. Onecould then use four anchoring lines, for example, each attached to aseparate anchor.

For anadromous fish species and marine breeds that thrive best in theupper water layers, only about 1/10 of the netpen volume will be locatedabove the water surface in the normal floating position. For breeds thatthrive better on deeper water, the netpen may be stabilized fullysubmerged at a desired depth, and this position then defines the normalfloating position of the netpen. The netpen may be adapted for a desireddepth through adjustment of the amount of water in the center pole 5 andthrough adjustment of the line lengths 28 and 42, and possibly 8. Thebuoys, which are attached to said lines 8, provides for practically allthe reserve buoyancy of the netpen in the normal floating position.Regardless of the carried species, the netpen, when required, forinstance during maintenance work or harvesting, may be elevated to asemi-submerged or approximately semi-submerged floating position bypumping air into one or more chambers in the center pole 5 in order toexpel any water therein.

The installation may be elevated to a semi-submerged position by pumpingair into the center pole 5 either through one or more tubes originatingfrom the external platform, alternatively from a boat at the surface, ordirectly from air accumulators located on the netpen. When theinstallation is used for open sea fish farming outside the skerries, thenetpen usually will have a large volume, e.g. 25000 m³, whichcorresponds to a diameter of approximately 36 meters, or 40000 m³, whichcorresponds to a diameter of approximately 42 meters. However, variousadaptions to the application (breeding, storage, and transport) andoperation site (open sea versus more sheltered areas) may result in anetpen volume that is greater or lesser than the above volumes. Theinitiation of the elevation or lowering of the installation may betriggered automatically or manually from the netpen or from an externalplatform or another floatation body, but may also be remotely controlledfrom an onshore facility by means of a bi-directional radio or satellitecommunication, for example. In addition, through such communicationsystem, information from sensors and cameras on and nearby theinstallation may be transferred to the platform and/or to an onshorefacility, which allows a high degree of long-distance monitoring of theinstallation and the fish.

When the installation is in a semi-submerged position, the working deck6 serves as a working platform on which personnel can reside forcarrying out work operations on the seine, inspection of theinstallation and the fish, gathering of dead fish, replacement of seinemodules, replacement of structure parts, and other tasks, see FIGS. 1-4,21-22, and 25-27. Before the working deck may be used by personnel foroperations on the installation, it must be lifted from a submergedposition underneath the installation (FIGS. 13 and 14) to a surfaceposition (e.g. FIGS. 1-4). This is accomplished by emptying one or morechambers in the buoyancy controllable stay 13, which may be a tube, forexample, of water using pressurized air. When the installation islowered down from the semi-submerged floating position, also the workingdeck 6 will be lowered down as the chambers are refilled with water.

The rotatability of the netpen will be made use of frequently inperforming the various work operations. Hence, the rotation isimportant, and is made possible as a result of that the netpen is onlyfastened at two opposing, permanent fixation points 14 integrated aspart of the center pole 5, see FIGS. 7-11 and 13-14. The actual rotationcan be accomplished, for example, by integrating a rim 18 in theterminal unit 14 and connecting a motor to this rim through a gear. Inorder to reduce the force that must be applied to the terminal units 14for rotating the netpen, it may be advantageous to make buoyancycontrollable one or more of the stays in the netpen framework, in whichcase the stays may be comparted into one or more chambers. Then, whenthe netpen is to be rotated, some of the chambers can be filled withwater, whereas other chambers, that already may be filled with water, isemptied of water.

The installation according to the present invention may be adapted fortwo in principle different requirements regarding level of technologyand extent of automation—a high-tech installation and a moderate or lowtechnology installation. In the high-tech case, the monitoring andadjustment of the installation will be a central task, and a number ofsensors and cameras will be located around the installation, both belowas well as above the water surface. All important data, as well ascamera images, can be transferred via radio, satellite, or a wiredconnection to the platform or some other floatation unit nearby theinstallation, or to an onshore facility from which personnel can monitorthe installation on a regular basis. When critical values are detectedfor one or more of the measured parameters, it is possible for theinstallation to automatically initiate submersion and other operations,while at the same time alarms are being triggered. However, in allnormal operation it is assumed that personnel arrive at the installationby boat and carry out the operations, either at the installation, fromthe platform, or by connecting to relevant tubes/cables in the lifeline(fodder, energy, air, communication link/data cables) from a boat. Thedifferent tubes and cables in the lifeline of the netpen may bedisconnected both at the netpen side and at the platform side, allowingthe cable and tube sections between the netpen and the platform to beindividually replaced. The moderate or low technology installation willbe less automated, having a correspondingly higher need for manualintervention.

FIG. 21 illustrates a method that may be used for harvesting the fish.The netpen is first elevated to a semi-submerged state. Thereafter, aseine 31 is attached on the inside above the cross section located abovethe water surface. The seine covers the entire (semi) cross section.When the netpen is rotated, the fish is trawled with the seine 31 andgathered together. The fish may then be raked or sucked aboard on avessel, possibly assisted by a tunnel system through which the fish isforced to swim when the volume is reduced. A seine may also be used thatdoes not cover the entire above water cross section, and that thereforedoes not gather up all the fish. A displacement medium other than aseine may also be used, such as a lattice. In addition, a sorting screenmay be installed, so that fish below a certain size will not beharvested.

The present invention consists of several parts, each part, includingone ore more characteristic features, forming the core in eachinvention. Polyethylene is of vital importance in the invention, and isnot chosen by chance. Polyethylene, or polythene which is the correctname, is a thermoplastic, or more exactly, a synthetic polymer, which isformed through a polymerization process wherein several ethylenemolecules joins to form long molecular chains. Thermoplastics arecharacterized in that they become soft and easily mouldable when heated.The plastic recovers its original properties when cooled down to normaltemperature. Polyethylene is available in various qualities.PolyEthylene Low Density (PELD) is soft and flexible. PolyEthylene HighDensity (PEHD) is harder and more stable, having a higher density(0.94-0.97 g/cm³). In selection of material, properties like density,yield point, elasticity module and fatigue resistance/strength, areimportant. Polyethylene, and especially PEHD, is excellent in thismanner. They possess a favorable density, extremely high strength inproportion to weight, high flexibility, and outstanding fatigueresistance. Moreover, the material has approximately the samecompressive strength value as tensile strength value, and it isinexpensive and easily workable. Polyethylene is not a new material inconnection with fish farming; it has been used within this industry formany years. However, the use of this material in marine structures ingeneral, and in fish farming installations in particular; has been verylimited. As construction material for fish farming installations, theuse of polyethylene has largely been limited to one or more horizontalfloatation rings at the surface, from which a seine is freely suspended.For other marine structures, the perhaps most important use ofpolyethylene has been as material in pipelines for water and discharge.In addition, the material has been used in some smaller rescue boats,oil booms, etc. However, polyethylene has not previously been used asconstruction material in large offshore structures, which is the case inthe present invention. Analyses and several model experiments hasindicated that the material is well suited for the purpose, both withrespect to strength related and practical considerations relevant to thefish and the personnel. The practical considerations include, forexample, the influence of the material on the response of the netpen,the maintainability and workability of the material, and its cost, whichare all considerations of particular importance to such offshorestructures. Thus, the results from analyses and testing of the presentinvention regarding the use of polyethylene as framework material may beparticularly interesting for larger manufacturing companies and theshipbuilding industry, wherein many actors, especially in high-costcountries, suffer from low influx of orders related to conventionalsteel industry.

The center pole 5 and its function both as a load bearing member for thestructure and as an adjustable floatation element for elevating andlowering the netpen, is also an essential feature of the presentinvention. The center pole preferably is made of steel, which is dueboth to its purpose, its positioning, and its disposition to a simpleconfiguration using standardized components. In particular, it isemphasized that the center pole most of the time will be located wellprotected from the cyclic and fatigue-promoting wave forces at thesurface since the normal floating position of the netpen is almost fullyor fully submerged, and also that steel can be a well suited materialfor essential constructional elements, also in terms of cost, as long asthey can be protected from large, cyclic wave loads and to a greatextent be standardized with respect to dimensions, shape and assemblyeffort.

Essential in the present invention is that the combination of design andconstruction materials is chosen so that the netpen as far as possiblewill conform to the natural forces instead of resisting them. By this ismeant a flexible and movable installation which to a significantlygreater extent than rigid and heavy installations, such as steelinstallations having a large half breadth area, follows the watermovement, and which is designed in such a manner that it resists largedeformations, that the relative load is smaller, and that forces aredistributed symmetrically in the structure. Model experiments have shownthat the netpen largely conforms to the above. In this connection, itshould be mentioned that a steel implementation of the netpen frameworkcould more than double the overall weight of the netpen, which wouldsignificantly reduce its response, leading to a correspondingly greaterrelative movement between the netpen and the fish, which is unfavorablefor the fish. In addition, the netpen would then be much moresusceptible to fatigue due to the steel stays located in the wave zone.

None of the main problems commonly encountered in the previous attemptsat open sea installations is found in the present invention; this isalso demonstrated through the above referred to model experiments ofthis netpen and through the figures and explanations in the descriptionherein. Such main problems include exposing the fish to stress andinjury due to the large relative movement between the installation andthe sea in waves, large volume reduction of the netpen due to largedeformations of the seine in rapid currents, failure of the supportingstructure due to fatigue, with a subsequent full or partial collapse, aswell as severe problems with accessing the installation for vessels andpersonnel and the ability of the personnel to reside on the installationin order to carry out the work, inspections and maintenance.

1. A netpen for breeding, storage, or transport of fish, the netpencomprising: a flexible framework of stays mainly composed ofpolyethylene materials containing fibers; a substantially horizontalcenter pole extending through the netpen and having sufficient stiffnessto serve as an attachment and supporting structure for the netpen, andwherein the center pole further serves as a buoyancy adjusting elementfor the structure through the adjustment of an amount of water and anamount of air in the center pole; and a substantially horseshoe-shapedtruss with a working deck attached at each end of the center pole, sothat the truss with the working deck may be used as a platform or hauntto support personnel performing work operations on the netpen when theinstallation is in a semi-submerged or substantially semi-submergedfloating position, a docking unit extending from the substantiallyhorseshoe-shaped truss, wherein the docking unit includes a plurality oftruss members, a plurality of fenders, and at least one element foradjusting the buoyancy through adjustment of the amount of water in theat least one element, so that the entire horseshoe including the dockingunit is arranged for being lowered to a position underneath the netpen,wherein: the netpen is lowerable into water when needed, the netpen ismoveable between a semi-submerged state for the performance of one ormore work operations and a fully submerged state, the netpen has theshape of a substantially dual curved body and is rotatable about asubstantially horizontal axis, and the substantially horizontal axisremains substantially horizontal in both the semi-submerged state and inthe fully-submerged state.
 2. The netpen of claim 1, wherein theframework further comprises a certain amount of at least anothermaterial.
 3. The netpen of claim 2, wherein the constituent partscomprises a fiber material.
 4. The netpen of claim 3, wherein the fibermaterial comprises carbon fiber.
 5. The netpen of claim 1, wherein thenetpen is sway anchored.
 6. The netpen of claim 1, wherein the netpen istension leg anchored.
 7. The netpen of claim 1, further comprising anexternal platform serving as a storage of life-supporting functions,said functions being transferred to the netpen through tubesconstituting one or more of the netpen lifelines.
 8. The netpen of claim1, wherein the netpen has a substantially oval shape, or a substantiallyspherical shape.
 9. The netpen of claim 1, wherein the netpen has asubstantially cylindrical intermediate section.
 10. The netpen of claim1, wherein the framework is covered by a seine formed of seine modulesor a grating formed of grating modules, wherein each seine or gratingmodule covers a separate window, each window being defined by the staysthat constitute the framework.
 11. The netpen of claim 10, wherein theattachment of the seine modules is accomplished by means of railsattached to the stays of the framework and rail engaging members mountedalong the edge of the seine module, the rail engaging members beingthreaded into the rails for keeping the seine module outstretched. 12.The netpen of claim 10, wherein the attachment of the seine modules isaccomplished by mounting rings along the edges of the stays and theseine, wherein a rope is threaded through these rings and tightened sothat the netpen is completely or almost completely enclosed by theseine, wherein excess seine along the sides of each seine module arefolded back over the connection and attached in a zip-fastener embeddedin the seine, so that the netpen is completely enclosed by the seine inorder to prevent the fish from escaping.
 13. The netpen of claim 1,wherein the polyethylene material comprises polyethylene low density(PELD) or polyethylene high density (PEHD).
 14. A netpen for breeding,storage, or transport of fish, the netpen being lowerable into waterwhen needed, the netpen being liftable to a semi-submerged state for theperformance of one or more work operations, and the netpen having theshape of a substantially dual curved body and being rotatable about asubstantially horizontal axis, the netpen comprising: a flexibleframework of stays mainly composed of polyethylene materials; asubstantially horizontal center pole extending through the netpen andhaving sufficient stiffness to serve as an attachment and supportingstructure for the netpen, wherein the center pole further serves as abuoyancy adjusting element for the structure through the adjustment ofan amount of water in the center pole; a substantially horseshoe-shapedtruss with a working deck attached at each end of the center pole, sothat the truss with the working deck may be used as a platform or hauntfor personnel performing work operations on the installation when theinstallation is in a semi-submerged or substantially semi-submergedfloating position; and a docking unit extending from the substantiallyhorseshoe-shaped truss, wherein the docking unit includes a plurality oftruss members, a plurality of fenders, and at least one element foradjusting the buoyancy through adjustment of the amount of water in theat least one element, so that the entire horseshoe including the dockingunit is arranged for being lowered to a position underneath the netpen.